The invention relates to a holding chuck for glass-working machines which can be fed with tubes and which are intended for producing small bottles, ampoules or the like, with several clamping jaws which are guided in a basic body and can be shifted to and fro by means of an actuating lever acting on a thrust ring, and which have, their ends facing away from the clamping surfaces, engagement means guided in slots in the thrust ring.
German Patent Specification No. 676,625 makes known holding chucks of the type in question, in which the slots in the thrust rings are formed by encircling grooves, into which engage projections arranged at the ends of the clamping jaws and formed either by parts of the clamping jaws themsleves or by crosspins fastened to the clamping-jaw ends. The known solutions are not entirely satisfactory, inasmuch as both the outlay involved in producing the chuck and that necessary for adjusting its clamping jaws are comparatively high, and they lack possibilities of compensating the play of the clamping-jaw guides after a lengthy period of use.